The rotary steerable drilling tool is an important part for implementing closed-loop steerable drilling and reflects the highest development level of existing rotary steerable drilling tools. The existing rotary steerable drilling tools are classified into push-the-bit and point-the-bit types according to steering ways and into dynamic and static types according to action ways of the bias unit. Compared with other rotary steerable drilling techniques, the dynamic point-the-bit rotary steerable drilling technique can keep the drilling tool at full-rotation states, so as to effectively reduce sliding friction resistance and enhance displacement extension and better hole quality. The dynamic point-the-bit rotary steerable drilling tool worked with LWD (Logging While Drilling) and high-precision downhole closed-loop control system can effectively increase drilling efficiency and rate of penetration, thereby gaining higher drilling economic benefits.
The invention, filed on Feb. 5, 1998 and approved on Jul. 25, 2000 by the name of Actively Controlled Rotary Steerable System and Method for Drilling Wells with the U.S. Pat. No. 6,092,610, discloses a dynamic point-the-bit rotary steerable drilling system. By designing the corresponding measuring and controlling systems, full-rotation drilling of the point-the-bit rotary steerable drilling tools is realized. In this invention, the point-the-bit steerable mechanism based on an offset mandrel can change continuously in structural bending angle from zero degree to the maximum degrees, and the structural bending angle can be kept constant by keeping the eccentric shaft geostationary. However, the drilling fluid passage is designed by means of annulus, at the same time, a signal processing method and a transmission mode of the sensor haven't been detailed, and the annulus fluid passage design method required complicated dynamic seal and reliability is hard to guaranteed.
The invention, filed on Apr. 19, 2002 and approved on Jan. 12, 2004 by the name of Rotary Steerable Drilling Tool with the EU patent No. EP 1258593B1, discloses a dynamic point-the-bit rotary steerable drilling system. In the rotary steerable drilling system, the housing directly drives the drilling bit to rotate and transmits drilling pressure in the meantime. But in this invention, it can be seen that the drilling fluid passage is made of a titanium alloy hose but without showing specific connection methods, power supply and signal transmission methods of internal sensors are not stated and a resolver used for measuring speed requires decoding.
The invention, published on Nov. 25, 2009 by the name of Point-the-bit Rotary Steerable Drilling Tool with Chinese Patent No. CN 101586440A, discloses a point-the-bit rotary steerable drilling tool widely applied in various stratums of different surface mechanical characteristics. The point-the-bit rotary steerable drilling tool is substantially a static point-the-bit rotary steerable drilling system. We can find its defects that a tool housing is fixed, drilling pressure and toque cannot be used to the greatest extent, and the structural bending angle is changed depending on adjustment of bending angle of a mandrel, which adds load to a motor and causes damage of the mandrel borne high-intensity alternating stress for a long time during adjustment of the structural bending angle.
The invention, published on Jan. 9, 2013 by the name of Offsetting Steerable Mechanism Design Method of Dynamic Point-the-bit Rotary Steerable Drilling tool with the Chinese Patent Publication No. CN 102865038A, discloses an offsetting steerable mechanism of a dynamic point-the-bit rotary steerable drilling tool. We can find its defects that the inner and outer eccentric rings of a double-eccentric-ring adjusting mechanism adopted in this invention are driven and adjusted by a servo motor, and the outer eccentric ring is embedded in the stabilized platform, thereby being not compact enough and adding design difficulty to a power supply mechanism of the stabilized platform; a conductive slip ring adopted in this invention supplies power for a power device but it will go wrong in case of violent vibration during drilling; absence of the pressure tubing in the drilling fluid passage requires dynamic seal in the positions of the coupler and the offsetting mechanism, which is substantially unreliable.
The invention, published on Feb. 6, 2013 by the name of Dynamic Point-the-bit Rotary Steerable Drilling Tool with the Chinese patent publication No. CN 102913131A, discloses a dynamic point-the-bit rotary steerable drilling tool and a control method thereof. But it still has its defects that the offsetting mechanism is driven by a hydraulic piston and is not compact enough, the axial displacement of the drilling bit shaft cannot be compensated when the offsetting mechanism is located in the maximum bending angle, and absence of the pressure tubing in the drilling fluid passage requires dynamic seal in the positions of the coupler and the offsetting mechanism, which is substantially unreliable; only the control method is included in this invention but specific mounting methods of the sensor are not mentioned; a conductive slip ring adopted in this invention supplies power for a power device but it is unreliable in case of violent vibration during drilling.
The invention, published on Sept. 4, 2013 by the name of Single-shaft Stabilized Platform Device Used for Rotary Steerable Drilling Tool and its Stabilizing Method with Chinese Patent No. CN 103277047A, discloses a single-shaft stabilized platform device and a stabilizing method thereof The single-shaft stabilized platform device is substantially a stabilized platform device used for a dynamic push-the-bit rotary steerable drilling system. However, it has its defects that a double-torque motor used for controlling the stabilized platform is complicated in structure; a force control method used in this invention is easy to cause speed fluctuation of the stabilized platform; working frequency of a non-contact electromagnetic coupler and distance between the primary side and the auxiliary side during mounting are not elaborated in its specification; power is supplied by a storage battery which is poor in durability and has limited operating time; signal transmission of the stabilized platform sensors depends on a non-contact high-frequency coupling transformer, signal modulation and demodulation are complicated.